This was the second year for this project, which will use biochemical and biophysical methods to examine conformational changes related to transport in glutamate transporters. These proteins are of critical importance in the central nervous system, where they play important roles in clearing neurotransmitters from synapses and in shaping the electrical activity of post-synaptic neurons. These transporters have been implicated as playing roles in a variety of diseases, including ALS, Alzheimer?s disease, and exitotoxicity. It is critical to understand the fundamental mechanisms by which there transporters function because such knowledge could lead to the development of therapeutic agents active against these proteins. We seek to analyze the dynamic movements of the functioning transporter on the way to a detailed understanding of its mechanism. Our approach is to analyze the details of transport in model glutamate transporters obtained from bacteria. These can be expressed and purified in large quantities and are amenable to biophysical methods not available for their mammalian cousins. In the past year we discovered that the bacterial glutamate transporters display a chloride transport activity which is stoichiometrically uncoupled from glutamate uptake. This chloride transport activity is similar to one which is important in the mammalian transporters and suggests that the bacterial homologs provide an excellent structural model in which to study the process of chloride transport in these proteins. We have also established the other ions which are coupled (and those not coupled) to transport in the bacterial proteins. In the upcoming year, we will start to use cysteine-scanning mutagenesis and site-directed fluorescence labeling to determine which parts of the molecule move during the transport process and characterize these movements in detail.